1. Field of the Invention
The present invention relates to a system, a method and others for detecting a user who attempts to fraudulently obtain user authentication of voice authentication technology.
2. Description of the Prior Art
FIG. 9 is an explanatory diagram of a mechanism of a conventional authentication device using voice authentication technology.
The emphasis has recently been on security measures in computer systems. In line with this trend, attention has recently been focused on biometrics authentication technology using physical characteristics. Among the biometrics authentication technology is voice authentication technology that uses differences of individual voice characteristics to identify/authenticate users. A conventional authentication device using such technology has the mechanism shown in FIG. 9.
Registration processing of feature quantity data showing feature quantity of voice for each user is performed in advance according to the following procedure. A user ID of a user to be registered is accepted and the user's real voice is captured. Feature quantity is extracted from the real voice and feature quantity data for the feature quantity are registered in a database in association with the user ID.
When a user authentication process is performed, a user ID of a user to be subject to the user authentication process is accepted and the user's real voice is captured to extract feature quantity of the real voice. The extracted feature quantity is compared with feature quantity indicated in feature quantity data corresponding to the user ID. In the case where the difference therebetween falls within a predetermined range, the user is authenticated. Otherwise, the user is determined to be a different person.
While various known technology is proposed as a comparison method of feature quantity, a text-dependent method and a free word method are typical methods. The text-dependent method is a method of comparing feature quantity by letting a user utter a predetermined phrase, i.e., a keyword. The free word method is a method of comparing feature quantity by letting a user utter a free phrase.
The voice authentication technology is convenient for users compared to conventional methods in which users operate keyboards to enter passwords. However, user authentication might be fraudulently attempted by recording voice surreptitiously with a recorder such as a cassette recorder or an IC recorder and reproducing the recorded voice with a reproducer. In short, the possibility arises of frauds called “identity theft/impersonation” or the like.
In order to prevent such deception, there are proposed methods described in Japanese unexamined patent publication Nos. 5-323990, 9-127974 and 2001-109494.
According to the publication No. 5-323990, a phoneme/syllable model is created and registered for each talker. Then, a talker is requested to utter a different phrase each time and user authentication is performed based on the feature quantity of phoneme/syllable.
According to the publication No. 9-127974, in a speaker recognition method for confirming a speaker, when the voice of a speaker is inputted, predetermined sound is inputted along with the voice. Then, the predetermined sound component is removed from the inputted signal and speaker recognition is performed by use of the resultant signal.
According to the publication No. 2001-109494, it is identified whether input voice is reproduced voice or not based on the difference of phase information between real voice and reproduced voice obtained by recording and reproducing the real voice.
The methods described in the publications mentioned above, however, involve complicated processing, leading to the high cost of hardware and software used for voice authentication.
If “identity theft/impersonation” in which surreptitiously recorded voice is reproduced to attempt to obtain authentication can be prevented in a simpler way, voice authentication technology will be used without anxiety.